The growth of CNG combustion powered vehicles and equipment is placing increasing needs for new means to fill dedicated, high pressure fuel storage cylinders used to power CNG engines. Current technology mobile CNG refuelers generally operate using pressure equalization methods (“cascading”) between the stationary storage and the target fill vessel, or using traditional gas compressors to provide continuous high pressure filling as the mobile CNG storage pressure decreases with each successive fill. The combustion driven compressor-based refueler can be run on the CNG itself or on other suitable fuels known in the art. However, the cascading strategy does not provide consistent high pressure output as the fixed storage is depleted and the corresponding pressure decreases. The prior art systems are also expensive and are often quite heavy, not lending themselves to all mobile applications.
Currently, most CNG powered engines have storage capabilities with a maximum storage pressure of 3,600 psig. As successive fills from the mobile refueler's storage bank are performed, the storage pressure in the mobile refueler's storage bank continues to decline. Prior art cascade filling methods do not provide any means to augment, or boost, the storage pressure to higher levels. As the pressure in the mobile refueler's storage tanks decreases below 3,600 psig, some means of increasing the pressure to 3,600 psig, such as for example, a compressor, is required.
Traditional compressors are often costly, require a relatively large footprint to be deployed, and are heavy. Additionally, traditional compressors require either external electrical power or some additional fuel storage if a combustion drive is used to power the compressor. However, in many locations where CNG powered equipment is operated, such as for example, locations that are remote or inaccessible, and/or not supplied with standard infrastructure (“stranded natural gas sites”), external power or compression equipment is not always available.
At many stranded natural gas sites, there is limited infrastructure to operate traditional compressors. Further, operating traditional compressors at such locations may not be economical due to low gas flow rates from the well. Additionally, steel tube trailers commonly used for CNG storage may find it hard to access the remote sites. Despite the growth of stationary CNG filling stations, there exists a growing need for portable filling equipment to refill CNG equipment storage tanks in more remote locations.